Cone and seed insects at Big Fork tree improvement area

2013·3 MB·English

by  Kegley, Sandy

Historic, Archive Document
Do not assume content reflects current
scientific knowledge, policies, or practices.

Forest Health
led Oy HEN oJey A]
Report 13-05 May 2013
CONE AND SEED INSECTS AT BIG FORK TREE IMPROVEMENT AREA
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D6K44 Sandy Kegley and Nancy Sturdevant
2013 |
Forest Health Protection, Coeur d’Alene and Missoula Field Offices
Introduction
Insects that feed on cones and seeds are common in our forests and can often become “pests”
in seed orchards where high value seed is collected from genetically superior trees. Douglas-fir
and western larch trees at Big Fork Tree Improvement Area (TIA) are now producing valuable
seed for reforestation. Demand for seed from east side Douglas-fir and mid- and high elevation
western larch is high and the Big Fork TIA is expected to provide seed for a large portion of
western and central Montana.
Low seed yields are occurring at Big Fork TIA and are at least partially due to Douglas-fir
tussock moth and western spruce budworm outbreaks causing defoliation and weakening the
trees as well as cone and seed insects damaging cones and consuming seeds. We report
insects found during the summer 2012 and provide management options to reduce seed losses
at Big Fork TIA in the future.
Methods
The Big Fork TIA is located on 80 acres north of Big Fork, Montana (PM, 7.27 N., R.20 W., sec.
14). It was visited June 4-5 and August 28-29, 2012. During each visit, cones with evidence of
insect frass or other damage were collected and either dissected on site or placed in rearing
containers at the Coeur d’Alene Forest Health Protection (FHP) lab. Any insects emerging in the
rearing containers were collected and identified. During the August visit, cones were examined
froma lift truck for insects that feed externally on cones and other signs of insect damage.
Numbers of damaged and undamaged cones for certain insects were tallied and percent
damaged cones calculated.
To monitor the flight period of fir coneworms, (Dioryctria abietivorella), Bill Crane, seed orchard
manager, placed coneworm pheromone traps in five Douglas-fir and three western larch blocks
United States Forest Northern 200 East Broadway
Department of Service Region P.O. Box 7669
Agriculture Missoula, MT 59807
on June 2. Lures were replaced July 6 and both traps and lures replaced July 30. Coneworm
moths caught were counted weekly through September 17.
Cones were operationally collected in late August and September and sent to the Coeur d’Alene
nursery for seed extraction. A portion of these seed were x-rayed to determine additional
damage by insects. Seed yield as pounds of seed per bushel of cones was determined.
Results
Insects Found
Western Spruce budworm
Western spruce budworm (Choristoneura
occidentalis) was found defoliating the Douglas-
fir and western larch blocks in the orchard and
was the most abundant insect reared from
damaged Douglas-fir and western larch cones
collected June 5 (fig 1). Budworms were found
to be a serious pest in Douglas-fir cones in 13
areas in Yellowstone National Park and
throughout Montana, including the Flathead
National Forest where Big Fork TIA is located
(Dewey 1970). Dewey found that budworms
damaged an average of 36-62% of Douglas-fir > w -_ ~—
cones (range 9-98%) in two consecutive years. Figure 1. Budworm larva in Dougl
Budworm larvae have also caused severe Fork Tree Improvement Area.
damage in western larch cones in western
Montana (Fellin and Shearer 1968).
Western spruce budworms overwinter as young larvae.
They typically emerge from hibernation from May to
June. Douglas-fir cones can begin developing before
lateral and terminal buds and are a good food source
for newly emerging larvae. Larvae feed on cones from
the time they emerge in the spring until they pupate.
Larger larvae in late stages of development are
voracious feeders and can damage more than one
cone. Budworm larvae complete their development by
mid- to late July and pupate within a cone or in the
foliage nearby.
Fir Coneworm
About 34% of cones examined from a lift truck in
Douglas-fir block 7A contained fir coneworm frass (fig.
2). Fir coneworm adult moths were reared from Figure 2. Coneworm frass on Douglas-
fir cone.
Douglas-fir cones collected June 5. Fir coneworms
were first caught in pheromone traps placed in
a
Douglas-fir orchard blocks on July 2 and in western larch on July 12 (fig. 3). Peak flights
occurred in mid-July and late August to early September.
| Traps placed June 2, 2012
e=me= Douglas-fir «*** Western Larch
Figure 3. Coneworm trap catches at Big Fork TIA in Douglas-fir and western larch orchard blocks.
The fir coneworm has a broad host range. It has been found infesting true firs, Douglas-fir, many
species of pine, spruces, western larch, and western hemlock in Canada, the northeastern
United States, and in the west from Alaska to northern Mexico (Sopow et al. 1996). Their life
cycle is variable but in general they have one generation per year. Adults begin flying in late
spring and are active until late summer. Larvae begin feeding in June and can be found in
cones throughout the growing season. Part of the population emerges as adults in the fall while
others overwinter as larvae or pupae on the cone or in the duff (Whitehouse et al. 2011).
Western Conifer Seed Bug
Western conifer seed bugs (Leptoglossus occidentalis) have been observed feeding on
Douglas-fir and several species of pine from British Columbia to Mexico (Koerber 1962). Adult
seed bugs hibernate over the winter—often invading people’s houses in the fall—and emerge in
spring. They are strong fliers and are easily disturbed. Mating and egg laying occur in late May
through early July. Eggs are laid in rows on needles. Seed bug nymphs look similar to adults
only smaller and with more orange on their abdomens. They are gregarious, do not have wings,
and do not fly. Both nymphs and adults feed on seed from the outside of cones. They have a
long, sucking beak (mouthpart) that they insert through cone scales to a seed. Seed contents
are dissolved by seed bug saliva and then consumed. Seed bug feeding causes partially filled
or empty seeds. Damaged seeds are not viable and can be detected by radiography or
‘biochemical marker based techniques (Lait et al. 2000, Bates et al. 2002).
Numerous seed bug adults and nymphs were found during examinations from a lift truck August
28 in western larch and in the Douglas-fir 7A block. Often multiple seed bugs were found on
each individual cone examined (fig. 4). Radiographs of extracted seed revealed partially filled
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seed damaged by seed bugs (fig. 5). Many empty seed were also found. Empty seed could be
due in part by seed bug damage or by lack ofM un eD but the cause cannot be discerned by
radiographs (Bramlett et al.1977).
=e 4. Adult = aN found on ES -fir cone (left) and western larch cone (dant) Seed bug nymph
(center) on Douglas-fir cone.
Douglas-fir Seed
Chalcid
Radiographs of seed
from Douglas-fir block
7A revealed
numerous seed
infested with Douglas-
fir seed chalcid
(Megastigmus
spermotrophus)
larvae (fig. 5).
Externally, infested
seeds look identical to
normal seeds and
have no visible
damage.
The Douglas-fir seed
chalcid emerges in
late May and June
from infested seed in
cones or seed on the
Figure 5. Radiograph of Douglas-fir 7A seed showing partially filled seed ground (Johnson and
damaged by seed bugs and seed chalcid larvae inside seed. Hedlin 1967). When
the adult emerges, an obvious clean-cut exit hole can be seen on the external seed coat. The
flight period lasts for about one month. The female inserts her ovipositor through the scales of
young cones to deposit an egg in the developing seed. Larvae remain in the seed consuming
the entire contents. It pupates in the seed. A portion of the population can remain in diapause in
the larval stage for more than a year (Hedlin et al.1980).
Douglas-fir Cone or Scale Midge
Midge larvae (Contarinia oregonensis or C.
washingtonesis) were found in some Douglas-fir
cones dissected on August 29 (figure 6). An adult
midge was reared from cones collected August
28 and will be sent to a specialist for
identification. The larvae of both species feed in
cone scales and can destroy seed. Larvae drop
to the litter and pupate. Adults emerge in spring
when Douglas-fir flowers are open for pollination
(Hedlin et al. 1980). Figure 6. Orange colored Douglas-fir cone
midge larvae.
Douglas-fir cone gall midge and seed chalcid have collectively destroyed 70% of Douglas-fir
seed from California, Oregon, and Washington. Damage was more serious in coastal rather
than inland areas (Schowalter et al.1985).
Douglas-fir Cone Moth
Douglas-fir cone moth (Barbara colfaxiana) is a common pest of Douglas-fir and has been found
in many locations in Montana (Dewey 1972). It is reported as a major pest in some areas.
Larvae can destroy 60-100% of the seeds in a cone. Infested cones may be misshapen with
frass on the surface or may have no external evidence of damage. Adult moths are similar to
coneworm moths but their fore wings are banded with brown, gray, and silver instead of only
gray and silver. They emerge in the spring and lay eggs on cone bracts. Larvae are white,
pinkish or yellowish. They pupate inside the cone and some may remain in extended diapause
for one or more years (Hedlin et al. 1980).
We found a pinkish lepidopteran larva in one cone dissected on August 28 that is likely the
Douglas-fir cone moth. However, no adults were reared out of any cones collected.
Other insects
Some small plant bugs (order Hemiptera) were reared out of western larch cones collected on
August 28. These bugs have not yet been identified and their role in cone ecology is unknown.
Seed Yield
The yield from Douglas-fir cones collected from breeding zone 7A at Big Fork TIA was 0.079
pounds of seed per bushel of cones (table 1) which is about 10 times less than the average
Douglas-fir yield of 0.5-0.8 pounds per bushel (Woody Plant Seed Manual USDA Ag Handbook
727). The yield from western larch cones collected ranged from 0.103-0.196 pounds of seed
2
per bushel of cones. Average yield from larch cones is a half a poundo f seed per bushel
(Woody Plant Seed Manual USDA Ag Handbook 727). The amount of this seed loss that is
caused by insects at Big Fork TIA is not entirely known. Other factors such as lack of viable
pollen can also reduce seed yield. However, the abundance of insects found at Big Fork TIA
and available literature on cone and seed insects indicate that insects are likely causing
considerable seed loss.
Table 1. Seed yield from cones collected at Big Fork TIA in 2012 (Coeur d’Alene Nursery Data).
Source ID Breeding Zone Lbs seed/ bushel
76 1% Te aa A ae |o s ace 0.079
The most important and damaging insects found in western larch cones at Big Fork TIA were
western spruce budworm, coneworms, and seed bugs. The most important insects found in
Douglas-fir cones were western spruce budworm, coneworms, seed bugs, and seed chalcids.
Management Options
The most effective method of controlling insects in seed orchards is using an integrated pest
management system which includes monitoring, sanitation (damaged cone removal),
pheromones (when available), and correct timing of insecticide treatments when needed.
Since many insects spend the winter inside damaged cones, removing these cones each year
will remove resident populations and should be done annually if possible. It may be difficult to
accomplish damaged cone removal in western larch because of the small size of the cones. In
addition, immigration of insects from any surrounding Douglas-fir, larch, spruce, or pine trees
could be a continuous problem.
Insecticide Treatments
Considering the low levels of seed production found at Big Fork TIA in 2012, spraying with an
insecticide should be part of an integrated pest management program developed for Big Fork in
the future. Single or multiple applications of synthetic pyrethroids (permethrin and
esfenvalerate) have been effective in reducing cone crop damage due to coneworms, seed
bugs, cone midges, and seed chalcids (Haverty et al. 1986, Sandquist et al. 1993). However,
multiple applications of these insecticides within a summer have sometimes led to outbreaks of
scale insects in the Coeur d’Alene western white pine seed orchard. Other contact insecticides,
such as carbaryl, would also likely be effective against many of the insects found.
Systemic insecticides can translocate into cones and kill cone and seed feeding insects while
avoiding most non-target insects. The systemic insecticide, emamectin benzoate, has been
shown to reduce the number of coneworm infested cones when injected into ponderosa pine
(Cook et al. 2013) and reduced Dioryctria populations in loblolly pine (Grosman et al. 2002).
However, while injecting systemic insecticides can useful in protecting cones of individual high-
value trees, it would not be practical to use to protect an entire orchard.
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Timing of insecticide applications is critical since many of the insects are protected once they
bore into the cones (unless using a systemic insecticide). Timing must coincide with insect
activity outside the cone which varies by insect species. Cone development has been used to
time insecticide treatments for cone midges, seed chalcids, and coneworms (Johnson & Hedlin
1967, Overhulser & Sandquist 1985). We can also use pheromone traps to help time
treatments (currently only available for coneworms). From 0 to 3 insecticide applications could
be required to achieve crop protection (Overhulser & Sandquist 1985). If only a single
application of insecticide is desired, Johnson & Hedlin recommend spraying when the cones are
pendent to half full length in development.
To protect against western spruce budworm damage, application of the insecticide needs to
coincide with Douglas-fir cone bud burst which is usually several weeks earlier than vegetative
buds. Spraying should be done when cones are about one inch long (when the seed cones
begin to elongate but before pollination is complete). The entire tree should be sprayed with
high-pressure spray equipment to reach the top and needs to be applied to all of the foliage to
the point of run-off (Stipe 1984).
Considering insect biology, pheromone trap data, and cone development, optimum timing of
insecticide treatment for the most important insects found at Big Fork TIA is shown in table 2.
Table 2. Optimum timing of insecticide treatment for
important cone and seed insects at Big Fork TIA.
Insect Target Timing of
x. “ee Insecticide Treatment
Coneworms Late-June to mid-July
or mid- to late-August
Seed Bugs June through Aug
Seed Chalcids 1 or 2 weeks after
cones turn pendent
Recommendations
Because of the importance of Douglas-fir and larch seed produced at Big Fork TIA and the
extent of insect damage found in 2012, we recommend at least two insecticide treatments in
2013—one in early June for spruce budworm and seed chalcids and one in mid-July for
coneworms and seed bugs. If necessary, a third treatment could be applied in August if
additional seed bugs are found.
Sanitation of damaged cones should occur whenever possible to remove any overwintering
insects. Monitoring coneworms with pheromone traps annually from June through early
September will help monitor population levels and in the timing of insecticide treatments.
FHP will continue to be involved in monitoring cone and seed insects, determining the proper
timing applications of insecticides, and conducting follow-up monitoring on treatment
effectiveness.
Acknowledgments
Seed yield and radiographs were provided by Dave Foushee, Supervisory Tree Improvement
Horticulturist and Jerri Park, Biological Science Technician at the Coeur d’Alene nursery.
Normal seed yield data was provided by Aram Eramian, Supervisory Forester, Coeur d’Alene
nursery.
Literature Cited
Bates, S.L.; Lait, C.G; Borden, J.H.; and Kermode, A.R. 2002. Measuring the impact of
Leptoglossus occidentalis (Heteroptera: Coreidae) on seed production in lodgepole pine
using an antibody-based assay. Journal of Economic Entomol. 95(4): 770-777.
Bramlett, D.L.; Belcher, E.W. Jr; DeBarr, G.L.; Hertel, G.D.; Karrfalt, R.P.; Lantz, C.W.; Miller,
T.; Ware, K.D.; Yates III, H.O. 1977. Cone Analysis of Southern Pines, A Guidebook.
USDA For. Serv. Southeastern Forest Exper. Sta. Gen. Tech. Rpt. SE-13. 28 p.
Cook, S.P.; Sloniker, B.D.; Rust, M.L. 2013. Using systemically-applied insecticides for
management of ponderosa pine cone beetle and Dioryctria coneworms in seed orchards.
Western Journal of Applied Forestry 28(2): 66-70.
Dewey, J. 1970. Damage to Douglas-fir cones by Choristoneura occidentalis. Journal of
Economic Entomology 63 (6): 1804-1806.
Dewey, J. 1972. A three year evaluation of Douglas-fir cone and seed insects in Montana and
Yellowstone National Park. USDA For. Serv. Northern Region Rpt. No. 72-1. 19 p.
Fellin, D.G.; Shearer, R.C. 1968. Spruce budworm larvae damage western larch cone and
— seeds. J. Forestry 66 (7): 568-570.
Grosman, D.M.; Upton, W.W.; McCook, F.A.; and Billings, R.F. 2002. Systemic insecticide
injections for control of cone and seed insects in loblolly pine seed orchards—2 year
results. Southern Journal of Applied Forestry 26: 146-152.
Johnson, N.E.; Hedlin, A.F. 1967. Douglas-fir Cone Insects and their Control. Canada Dept. of
Forestry and Rural Development. Forestry Branch Dept. Pub. No. 1168. 11 p.
Haverty, M.I.; Shea, P.J.; Stipe, L.E. 1986. Single and multiple applications of fenvalerate to
protect western white pine cones from Dioryctria abietivorella (Lepidoptera: Pyralidae). J.
Econ. Entomol. 79:158-161.
Hedlin, A.F.; Yates Ill, H.O.; Tovar, D.C.; Ebel, B.H.; Koerber, T.W.; and Merkel, E.P. 1980.
Cone and Seed Insects of North American Conifers. Canadian Forestry Service, USDA
Forest Service, Secretaria de Agricultura y Recursos Hidraulicos, Mexico. 122 p.